An electrical machine may have distributed windings or concentrated windings, the difference between these windings being well known to those of ordinary skill. In a concentrated winding machine, a stator may be constructed in segments, which are then connected to form the entire stator. This is illustrated in FIG. 1, which is a sectional diagram illustrating a conventional segmented stator 500 that is composed of a number of stator segments 510. Each stator segment includes an integral tooth 512 and teeth tips 515. The teeth 512 define stator slots 520 that lie between adjacent teeth. Each stator segment 510 is in contact with an adjacent stator segment 510 at one radial end, while at the other radial end the teeth tips 515 of the teeth 512 are separated by a distance 505. The distance 505 may also be referred to as a slot opening.
Conventional stator designs include fixed-tooth stators and loose-tooth stators. For purposes of this disclosure, a fixed-tooth stator is defined as a stator that does not allow for the movement of stator teeth with respect to one another. The segmented stator 500 may be referred to as a fixed-tooth stator because the stator 500 is assembled such that the individual stator segments 510 are joined in a way that does not allow stator teeth 512 to move relative to one another. Conversely, loose-tooth stators allow for the movement of stator teeth with respect to one another. Examples of loose-tooth stators may be found in U.S. Pat. No. 6,844,653 to Kolomeitsev et al., issued Jan. 18, 2005, entitled “Stator design for permanent magnet motor with combination slot wedge and tooth locator,” which is incorporated by reference.
Before the segmented stator 500 is assembled, the individual coils that are wrapped around each stator segment 510 are formed by winding around a bobbin, which is typically made of plastic. The plastic bobbin functions as a slot liner that isolates the winding from the stator lamination (iron). FIG. 2 is a sectional diagram illustrating a conventional stator segment 620 having a coil 630 wrapped around a plastic bobbin 640.
A disadvantage to using the plastic bobbin 640 as a slot liner is that it reduces the slot fill. That is, because the plastic is relatively thick, it decreases the volume in the stator slot that could otherwise be occupied by turns of the coil 630. Although paper insulation slot liners are thinner than plastic slot liners, paper insulation slot liners cannot be used in conventional segmented stator construction because bobbin style winding is not possible as the paper is often twisted or cut as the coil is wound around the paper. Also by filling the slot with more copper (thicker conductor), copper loss can be reduced. Reduced copper loss enables improved thermal performance of the machine.
To solve this problem of segmented stator construction, stator teeth can be inserted in a continuous stator back ring. FIG. 3 is a sectional diagram illustrating another conventional fixed-tooth stator 700 that is constructed by inserting stator teeth 720 in a continuous stator back ring 710. Like the stator teeth 512 of FIG. 1, the stator teeth 720 define stator slots 725 between adjacent teeth, and the stator teeth have teeth tips 715 that define a small gap or slot opening 705. In this construction method the coil is wound separately from a stator tooth 720. Afterwards, a paper insulation slot liner may be placed around the teeth, and then coil is slid over the end of the stator teeth 720 that do not have the teeth tips 715. Afterwards, the same end of the stator tooth 720 (the one without the teeth tips 715) is inserted in a corresponding slot on the stator back ring 710 to form the stator.
However, a disadvantage to the method of stator construction illustrated in FIG. 3 is that it weakens the stator mechanical structure and lowers its stiffness. Therefore, compared to the segmented stator construction method illustrated by FIG. 1, this method is more susceptible to undesirable vibration and noise.
Accordingly, it is desirable to have a fixed tooth stator that can take advantage of paper slot liners to increase slot fill. In addition, it is desirable to have a fixed tooth stator with increased stiffness. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.